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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2008.05.016 Byline: Marco Vannini, Elisabetta Lori, Cecilia Coffa, Sara Fratini Abstract: Individuals of Cerithidea decollata periodically migrate along mangrove trees, resting on the trunks during high water, and foraging on the surrounding muddy platform during low water. Groups, ranging from tens to hundreds of snails, aggregate on the trunks well before the incoming tide (1-2h) at a level that will not be reached by the high tide, that is, from a few centimetres (around neap tides) to over 1m (around spring tides) above the ground. We addressed two questions: (1) how can snails determine when to stop climbing and (2) how do snails determine the length of the path necessary to stop at that level. We used plastic pipes, 2m long and 20cm in diameter, along which snails crawled just as on their own trees. Experiments in which the pipes were lowered, raised or tilted indicated that snails were able to perform both tasks. Overloading the snails with lead weights showed that the estimate of the required travelling distance was probably related to the energy used to cover that distance. However, it was not possible to define how snails were able to establish the distance they needed to travel to avoid the incoming tide, although we were able to exclude any role of for visual cues or chemical marks present on substratum. Author Affiliation: (a) Department of Evolutionary Biology 'L. Pardi', University of Florence, Italy (a ) Zoological Museum of the University of Florence, 'La Specola', Italy (a ) Department of Evolutionary Biology, University of Siena, Italy Article History: Received 9 January 2008; Revised 26 March 2008; Accepted 6 May 2008 Article Note: (miscellaneous) MS. number: D-08-00018

The ability for climbing crabs of East African mangrove swamps, Sesarma leptosoma, to recognize predators visually is examined by experimentation with three dummy objects made to look like the predators. The results show that the crabs hesitated in their movements when confronted with the dummies which had the open claws of the predator. From this it can be concluded that the crabs are able to visually detect shapes and sizes and the presence of danger.

A swimming crab was studied to determine if it used landmarks to locate its refuges.